1 February 1986 Catadioptric Afocal Telescopes For Scanning Infrared Systems
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Optical Engineering, 25(2), 252319 (1986). doi:10.1117/12.7973823
Reflecting and catadioptric lenses have been used in astronomical telescopes for many years. More recently, among other applications, they have been widely used in large-aperture and man-portable image-intensified night vision equipment. The afocal telescope used with a scanning infrared system operating in the 8 to 12µm wave-band is required to match the large field of view and small aperture of the scanner with the small field of view and large entrance aperture required for long-range observation. The telescope construction used is usually a refracting telephoto. This can be configured either as a single field of view lens, as part of a dual or multiple field of view switchable system, or as the basis for a mechanically or optically compensated zoom system. However, for large, high magnification telescopes, catadioptric systems can offer advantages over refractors. Two types of catadioptric lens are described. The first has a "low" magnification (7.5 x ) and utilizes a full aperture germanium lens to correct spherical aberration. The second has a "high" magnification (30 x ) and uses a subaperture germanium element to correct the same aberration.
David G. Norrie, "Catadioptric Afocal Telescopes For Scanning Infrared Systems," Optical Engineering 25(2), 252319 (1 February 1986). https://doi.org/10.1117/12.7973823

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